It is the purpose of this study to determine the degree and nature of the interaction of low megahertz ultrasound and mammalian tissues. Ultrasound is now very widely used clinically both in diagnosis and in therapy. In both of these medical applications the opportunity for reproductive tissues to become exposed to significant levels of ultrasound for appreciable periods of time is extant. Studies have not been undertaken to determine the interactions that could occur and to determine whether or not cautions should be extended to those perpetrating and those receiving exposure. For these reasons the mammalian ovary has been selected as the specific organ for investigation in the proposed study. This study will involve determining threshold levels at which functional and/or structural changes occur to murine corpora lutea. Following identification of thresholds and measurement of absorption coefficients, a second dose-effect study will assess multiple exposures. Subsequent to these studies an electron microscopy study and a fertility study will be completed. It is expected that the results of this study will provide a basis for assessing risk incurred by ovarian tissues during exposure to ultrasound at therapeutic and at diagnostic levels and regimes.